The present invention relates to fluid coupling devices of the type including valve means operable to control the quantity of fluid in the fluid operating chamber, and more particularly, to such devices of the type including a valve element which is actuated to rotate in a plane parallel to a member which defines a fill opening.
Although the present invention may be used advantageously in fluid coupling devices having various configurations and applications, it is especially advantageous in a coupling device of the type used to drive a radiator cooling fan of an internal combustion engine, and will be described in connection therewith.
Fluid coupling devices of the viscous shear type have been popular for many years for driving engine cooling fans, primarily because their use results in a substantial saving of engine horsepower, resulting from the fact that the coupling operates in the engaged condition only when cooling is needed, and operates in a disengaged, relatively lower speed condition when little or no cooling is required. The change between the engaged and the disengaged conditions occurs in response to the sensing of ambient air temperature by a bimetal coil, which rotates the valve member to either cover or uncover the fill opening, thus controlling the flow of viscous fluid from a reservoir chamber into an operating chamber
In fluid coupling devices of the type to which the present invention relates, the quantity of fluid in the operating chamber is controlled indirectly, i.e., the angular position of the valve arm controls the radially outermost point of overlap between the valve arm and the fill opening, thus controlling the radial dimension of the fluid meniscus contained in the reservoir chamber, which determines the volume of fluid in the operating chamber.
In a number of relatively high-torque coupling devices, in order to obtain the desired relationship between the fluid fill rate and changes in temperature, it has been necessary to provide a pair of fill openings. Typically, when there is a pair of fill openings, they are identical in size, shape, and location (i.e., relative to the axis of rotation of the device), although such identity of the fill ports is not an essential feature of the present invention. It has also been typical for such a pair of fill ports to be oppositely disposed (i.e., 180 degrees apart), about the axis of rotation of the device. Such an arrangement has been conventional for a number of reasons, including uniform distribution of fluid entering the operating chamber, as well as the ability to use a simple, rectangular valve arm configuration.
One of the problems associated with dual fill port devices is the difficulty of assembling and calibrating the cover and valve subassembly. The term "calibration" as used herein refers to achieving the proper position of the valve arm, relative to the fill ports, for any particular temperature condition. This is typically accomplished by means of a water bath calibration in which the cover subassembly is placed such that the bimetal element is in a water bath of a known temperature, and the valve plate (which defines the fill openings) is rotated to a position in which the edge of the valve arm is aligned with a calibration mark on the valve plate. Ideally, if the fill openings are identical, the relative position of each fill opening and the valve arm should be identical, which should occur if all of the various parts involved are machined accurately and are concentric relative to each other. However, such is frequently not the case, and if the operator makes the proper calibration at one fill opening, the other fill opening and the valve arm are in a substantially different relationship. The operator may then either leave the valve plate in that position, or move the valve plate to a position in which the valve arm will be offset from the calibration mark, such that the amount of offset at the two fill openings will be about the same. In either case, the result will be an incorrect relationship between ambient temperature and the position of the valve arm relative to the fill openings. Depending upon the direction of the error, this may, in turn, result in the coupling device engaging at too low a temperature, thus wasting engine horsepower and creating excessive noise, or may result in engagement at too high a temperature, with the attendant possibility of the engine overheating.